simpledb.query
Class ConstantExpression

java.lang.Object
  simpledb.query.ConstantExpression

All Implemented Interfaces:

Expression

public class ConstantExpression
extends Object
implements Expression

An expression consisting entirely of a single constant.

Author:

Edward Sciore

Constructor Summary

ConstantExpression(Constant c)
Creates a new expression by wrapping a constant.

Method Summary

boolean	appliesTo(Schema sch) Returns true, because a constant applies to any schema.
Constant	asConstant() Unwraps the constant and returns it.
String	asFieldName() This method should never be called.
Constant	evaluate(Scan s) Returns the constant, regardless of the scan.
boolean	isConstant() Returns true.
boolean	isFieldName() Returns false.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ConstantExpression

public ConstantExpression(Constant c)

Creates a new expression by wrapping a constant.

Parameters:

c - the constant

Method Detail

isConstant

public boolean isConstant()

Returns true.

Specified by:

isConstant in interface Expression

Returns:

true if the expression is a constant

See Also:

Expression.isConstant()

isFieldName

public boolean isFieldName()

Returns false.

Specified by:

isFieldName in interface Expression

Returns:

true if the expression denotes a field

See Also:

Expression.isFieldName()

asConstant

public Constant asConstant()

Unwraps the constant and returns it.

Specified by:

asConstant in interface Expression

Returns:

the expression as a constant

See Also:

Expression.asConstant()

asFieldName

public String asFieldName()

This method should never be called. Throws a ClassCastException.

Specified by:

asFieldName in interface Expression

Returns:

the expression as a field name

See Also:

Expression.asFieldName()

evaluate

public Constant evaluate(Scan s)

Returns the constant, regardless of the scan.

Specified by:

evaluate in interface Expression

Parameters:

s - the scan

Returns:

the value of the expression, as a Constant

See Also:

Expression.evaluate(simpledb.query.Scan)

appliesTo

public boolean appliesTo(Schema sch)

Returns true, because a constant applies to any schema.

Specified by:

appliesTo in interface Expression

Parameters:

sch - the schema

Returns:

true if all fields in the expression are in the schema

See Also:

Expression.appliesTo(simpledb.record.Schema)

toString

public String toString()

Overrides:

toString in class Object